For some people, global warming is a hard sell. Temperatures going up by a few degrees doesn't sound all that bad, and even results like drought or increased spread of mosquitos and other pests, while certainly unpleasant, are familiar issues. Mega-problems like whiplash/abrupt climate change, where warming leads to an ice age, can sound more surreal than threatening. But this website might change their minds. It shows something that is obviously warming-related, is already starting to happen (not just a "might happen 50 years down the road" possibility), and is a clear danger to the industrialized world's economies and societies: a seven meter rise in sea levels.

Flood Maps mashes up NASA elevation data and Google Maps, and offers a visualization of the effects of a single meter increase all the way to a 14 meter rise. The default increase of seven meters -- about 23 feet for those who avoid the whole metric thing -- is the amount the world's oceans will rise once Greenland's glacial ice pack melts completely. This melting is already underway, and is happening with startling speed.

[From February:] ... researchers found that [Greenland's] glaciers were traveling faster than anyone had predicted. They also determined that even more northerly glaciers were on the move and that in just 10 years the amount of fresh water lost by all the glaciers had more than doubled from 90 cubic kilometers of ice loss a year to 224 cubic kilometers. "The amount of water Los Angeles uses over one year is about one cubic kilometer," Rignot points out. "Two hundred cubic kilometers is a lot of fresh water."

The map doesn't cover the whole world yet, but does cover most of North America and the Caribbean, as well as most of Western and Central Europe. As expected, a seven meter rise inundates locations like the Netherlands, Louisiana and Florida; perhaps surprisingly, areas like southeast England and inland regions east of San Francisco, while not often thought of as being at risk from rising seas, suffer just as much. Since the site uses Google Maps, you can view the results in both standard map and satellite format -- and seeing the projection of the oceans approaching the doors of (for example) the White House can be sobering.

The amount of sea level rise coming from melting ice sheets today is fairly low: a bit less than a millimeter every year. Another millimeter or more comes from the "thermal expansion" of warmer water. But this amount is very clearly just the pebbles before the avalanche; although it's unlikely that we'd see the full seven meter increase as an abrupt event, as the glaciers melt faster and faster, the oceans will rise more and more. A one meter rise is a distinct possibility within the next couple of decades; seven meters could come far faster than we would expect, or be able to handle.

What makes this all the more troubling is that Greenland isn't the only place that glaciers are melting; the Antarctic glaciers are, too. And there's a helluva lot more glacial ice on Antarctica than on Greenland. If all of the Antarctic ice were to melt off -- an extraordinarily unlikely event, fortunately -- sea levels would go up by 60 meters.

We live in a post-Katrina world. We have graphic evidence of what it looks like to have a city nearly destroyed by the weather. Even people safe in regions distant from the oceans now know what kind of damage losing just one major city can do to a nation; imagine what damage to every major coastal city would do.

Now that is cool - exactly what I was hoping somebody would do a few months back! I just took a look at Long Island where I live - the South Fork (Hamptons etc) becomes it's own little island with just a 4 meter rise...

Brilliant. Been looking for this for years. The sad bit is that I've watched the "worst case" scenario go from 2 to 7 meters in less than a decade. And it ain't done going up.

New data that just came out from a couple of mass-measuring satellites nicknamed "Tom and Jerry" demonstrate that one the presumptions climatologists have been working under -- that Antarctic ice loss at the edges was offset by snow accummulation over the continent -- is wrong. Antarctica is suffering a net ice loss.

Me, I live in Amsterdam. It won't take more than 2 meters before I'm packin the kids into a canoe.

The base calculations of sea level rise (1 m this century, etc.) are due to thermal expansion of the vast quantity of ocean water. The magnitude of thermal expansion would be trivial for most enclosed bodies of water.

The big rises (seven meters, etc.) would be due to the melting of ice masses, also affecting oceanic sea levels but not other water bodies.

The risk to river levels (other than those tidally influenced) and lakes would be due to precipitation changes, which are only now being modeled with some confidence at regional levels. The Climate Impacts Group at the University of Washington has some good information on this.

Short answer: there are a few big phenomena that will largely drive sea levels, and a multitude of medium-scale and local phenomena that will influence river flows and lake levels. Easier to play with the former to make maps.

Posted by: Ted on 23 Mar 06

I have always wondered; where the big rises as Ted mentioned are due to melting ice masses. If the majority of these are in the ocean already, and therefore mostly submerged and ice displaces more than water in a liquid state. Isn't the threat of rising oceans overstated?

To be clear, I am not denying the threats of global warming or rising ocean levels from thermal expansion, but unless the vast majority of the ice on the planet is currently not submerged, the Waterworld scenarios violate my senses.

Posted by: Don on 23 Mar 06

I'm glad you asked that, Don, because that's a common misperception. The concern isn't over icebergs melting -- as you say, that would be a zero net change result -- but over the melting of glacial ice that's on land, with the water then running into the ocean.

And as the pull quote in this post suggests, there's a *lot* of water locked up in glaciers on land.

I noticed that some inland lakes -- such as the Salton Sea in Southeast California. Because there is not outlet from the Salton Sea (at least, I don't think there is), why is it show as rising? Thanks -- this is a terrific site!

Posted by: Onlywayne on 28 Mar 06

A 3 meter rise was a likley result of surging [ sliding] of antartic ice already lubricated by water at its base. It has been longer in coming than I expected from what Nigel Childer wrote. Things are finally happening after 15 years when I was teaching this.

Posted by: Dennis Gwynn on 28 Mar 06

The average global thermal change going from ice age to interglacial temperatures is only 4 degrees. Sounds familiar does it not? This time it was from a higher starting temperature.

The other part of this is that temperature drops initiating ice ages have taken place in less than a century. We do not know why it happened, but it is suspected that something associated with global warming causes it. Those who survive the flooding will find out.

Posted by: dennis gwynn on 28 Mar 06

response to Deniel: The map author probably just included height data for a certain range from the coast, so I'm sure there are plenty of innacuracies as to where water would actually flow if the oceans reached that height.